This is how heatwaves affect your body - and your mind

Every year, more than a billion people sweat their way through India and Pakistan’s gruelling summer heatwaves. These usually begin towards the end of May, but this year the heat arrived unusually early and hit with sweltering force.

The average maximum temperature for central India in April was the highest since records began 122 years ago. The mercury reached 37.78C, according to the Indian Meteorological Department. Neighbouring Pakistan also bore the brunt of the extreme heat. Some cities in the southeastern Sindh province recorded highs of 47C at the end of April.

Experts say the climate crisis will cause more frequent and longer heatwaves, affecting more than a billion people across the two countries. "This heatwave is definitely unprecedented," said Dr Chandni Singh, Lead Author at the Intergovernmental Panel on Climate Change, “and it will have cascading impacts on health,” he said.

Very hot days can lead to dehydration, heat exhaustion and, in the worst cases, heatstroke. Heat exhaustion is not usually serious if a person can cool down within 30 minutes. But if it turns into heatstroke it needs to be treated as an emergency. Children, the elderly and people with long-term health conditions like diabetes and heart problems are more at risk of both heat exhaustion and heatstroke.

Hot days “are also associated with a higher risk of a number of other conditions that are not typically thought to be heat-related, such as kidney problems, skin infections and pre-term birth among pregnant women,” according to a professor at Boston University. “In fact, heatstroke, heat exhaustion and dehydration account for a relatively small fraction of the total health risks associated with days of extreme heat,” he said.

A growing body of evidence also suggests that days of high temperatures may negatively affect mental health. A study in New York found that hot days were associated with higher risk of hospital visits for substance abuse, mood and anxiety disorders, schizophrenia and dementia. Other studies show that hot weather is linked to lower performance on standardized tests.

Joshua Goodman, a Professor of Education and Economics at Boston University, said the findings on heatwaves and extreme heat scenarios have major implications for students who attend classes in buildings that lack proper ventilation and air conditioning. “There are countries where students experience 200 days a year where the temperature is over 80 degrees Fahrenheit (26C),” said Goodman, adding that there is an “important component of learning differences between countries, mainly due to the fact that it is literally just harder to learn when you live in a hot place”.